It is impossible to detect all wavelengths with a single detector in a general spectrophotometer covering a wide wavelength range as aforementioned. Therefore, conventionally, the wavelength range has been properly divided into plural regions on the basis of the frequency, and different detectors have been provided for the respective regions. In many cases, a photomultiplier tube (PMT) is utilized for the ultraviolet-light region and the visible-light region, while a PbS (plumbous sulfide) detector is utilized for the near-infrared light region. In some cases, respective wavelength ranges may be further divided into plural regions, and detectors of the same type having different characteristics may be used for sharing the respective partial regions. For example, JP-A No. 2002-62189 describes an example of employing two PbS detectors having different spectroscopic sensitivity characteristics for sag the near-infrared-light region.